The invention concerns a speed control device for an electronically commutated multiphase electric motor. These types of speed control devices are used in combination with permanently excited electronically commutated multiphase electric motors in motor vehicles, particularly for fan drives or pump drives with a relatively small starting load moment.
U.S. Pat. No. 5,563,481 discloses a speed control device for electronically commutated multiphase electric motors with adjustable speeds, in which the pulse width of the supply voltage is modulated by means of a high frequency, inaudible 20 kHz pulse. U.S. Pat. No. 5,589,745 discloses a second speed control device which provides pulse width modulation of the supply voltage by means of a drive circuit with pulse groups that can be adjusted with respect to amplitude and/or duration. However, these known speed control devices require complex hardware and/or expensive software.
British Laid-Open Publication GB-OS 1 563 015 (which corresponds to German Laid Open Publication 26 39 055 B2), U.S. Pat. Nos. 4,283,664, and 3,769,555 disclose speed control devices for electronically commutated electric motors having motor phases that can be powered unidirectionally and unpulsed during definable time blocks by phase shifters from a constant voltage supply, depending on rotor position sensor signals, thereby creating torque.
For the device of GB-OS 1 563 015, various speeds can be achieved by the assignment of definite pulse patterns to defined speeds. U.S. Pat. No. 4,283,664 provides for setting various speeds by adjustment of the constant voltage supply source. U.S. Pat. No. 3,769,555 permits the setting of various speeds by means of a pulse generator that adjusts pulse width and pulse frequency.